Grid support



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w. J. FARRELL GRID SUPPORT Filed Feb. 2, 1943 /000 A50 O a! 000 00 30 00 3500 4040 Ho uns INVENTOR. IV//bm L/ Far/e @Maux (5 1MM@ Patented June 13, 1944 GRID SUPPORT William J. Farrell, Parlin, N. J., assigner to Hercnles Powder Company, Wilmington, Del., a

corporation of Delaware Application February 2, 1943, Serial No. 414,436

3 Claims.

This invention relates to the use of particular alloys in the construction of a grid support for the catalyst gauze used in the manufacture of nitric acid by the ammonia oxidation process.

The conversion of ammonia to nitric acid is carried out at a temperature of about 900 to 950 C. by passing a mixture of ammonia and air through a, catalyst consisting of a number of layers of a catalyst gauze,such as platinumrhodium gauze. The gauze is supported horizontally on a circular metal grid which in many installations is about 14 inches in diameter. 'I'he perimeter oi' the metal grid rests on a ledge on the inside of the oxidation unit at apoint near the top. The grid is usually constructed in two halves. At the high temperature to which it is exposed, the grid deteriorates and buckles in time requiring frequent replacements to insure that the catalyst gauze may lie flat and the gas mixture pass entirely through it.

Many attempts have been made in the past to make this grid support of an alloy which is particularly resistant to deterioration under the particular conditions of the ammonia voxidation process. Examples of such alloys which have been used include chrome steels such as 1B chrome-8 nickel and 25 chrome-20 nickel; nickelmolybdenum-iron alloy of about a 62-30-5 parts ratio; nickel-molybdenum-chromedron alloy of about a 58-17-15-6 parts ratio; and cast alloy composed primarily of nickel and silicon plus small amounts of other catalytic elements. These have al1 been found to deteriorate or buckle badly in a relatively short time (3 to 4 months).

Now in accordance with the present invention, it has been found that a catalyst grid support of high resistance to deterioration may beanade of an alloycbmprising cobalt, chromium and tungsten in about a 55-33-6 parts ratio. This alloy is known'tothe trade as Stellite 6 and is manufacturegivby the Haynes-Stellite Company.

Havingy indicated in a general way the nature and purpose of the invention, there follows a more detailed description of preferred embodiments thereof with reference to the accompanying drawing in which is shown'in Figure l a perspective view of a typical circular grid catalyst support commonly used in the manufacture of nitric acid by the ammonia oxidation process. 'Ihe catalyst support usually comprises two halves, the circumference of which is cast in separated portions. The circumferential portions are held together by reinforcing bars sufficiently separated to allow the passage of the gas and forming a convex surface on one side of the support and a fiat surface on the other.

The graph shown in the drawing at Figure 2 illustrates a comparison between various composition resistant alloys which have been tested and the cobalt-chrome-tungsten alloy of the present invention. In the graph, the per cent loss in weight is plotted against the number of hours that the sample of the alloy was exposed to the ammonia oxidation conditions. yFrom the graph, it will be seen that the cobalt-chrometungsten alloy of the present invention is highly superior to any of the others shown, having, for instance, lost 0.5% of its weight after over 2000 hours of exposure to the ammonia oxidation conditions. It will be seen that the next base alloy tested, that is, chrome-nickel (Z5-20) steel loses over 3% or more than six times as much of its weight under the same conditions.

The following are the experiments results upon I which the graph was based and serves to demonstrate the definite and unexpected superiority of the cobalt-chromium-tungsten alloy of the present invention:

Hours in Per can service t loss Nickel-molybdenum-iron alloy (2-30-5 parts 281 8.50 ratio) 324 8. 324 2. 64 Chrome-nickel (1843 parts ratio) steel ggg 1g: 1, 699 19. 52 i 324 o. tu Nickel-molybdenum-chromedrmi alloy (58- 626 2. 74 17-15-6 parts ratio) 907 6. 34 l. 699 15. 58 604 0. 45 863 0. 82 Cobalt-chromium-tungsten-iron alloy (S0-30- l, 511 3. 21 10-20 parts ratio) l, 770 4. 70 2, 072 6. lil 2, 39s 9. o4 324 0. 23 si is Chrome-nickel (2S-20 parts ratio) steel l, 690 3. i4 2, 304 31 2. 758 6. 75 3, 212 7. 76 302 0. 02 604 0. 02 863 0. 02 1, 511 D. 07 Cobalt-chrome-tungston (55-33-6 parte ratlo)-. ggg g 2. 396 i. 24 3, 001 l. 62 3, 456 2. i3 3. 909 2. 28

While the particular alloy of the present invention has been described above as cobalt-chrometungsten (55-33-6 -parts ratio). the alloy is that which is known to the trade as Stelllte 6, a product of the Haynes-Stellite Company. The exact composition is not disclosed by the Haynes- Stellite Company, but it is a composition reasonably equivalent to that described above. Besides the above description, it is known that the com .position is substantially free of iron.

Thus, the present invention has described a new and useful alloy which comprises cobaltchrome-tungsten in about a 55-33-6 weight ratio which when used in the construction of a grid support for the catalyst in an ammonia oxidation converter has an excellent resistance to deterioration.

What I claim and desire to protect by Letters Patent is:

1. In an ammonia oxidation converter. a combination of a wire gauze catalyst suitable for ammonia oxidation mounted on a grid support comprising a cobalt-chrome-tungsten alloy substantially free of iron.

2. In an ammonia oxidation converter, a combination of a wire gauze catalyst suitable for ammonia oxidation mounted on a grid support comprising a cobalt-chrome-tunssten alloy in about a 55-33-6 weight ratio, said alloy being substantially iron free.

3. In an ammonia oxidation converter, a combination of a wire gauze catalyst suitable for ammonia oxidation mounted on a grid support comprising two semicircular grids ot a. cobalt-chrometungsten alloy in about a 55-33-6 weight ratio, said alloy being substantially iron free.

WILLIAM J. FARRELL. 

